Allow Google Update to impersonate the client for on-demand update checks.
Allow Google Update to impersonate the client for on-demand update checks.

This is a speculative fix for ERROR_BAD_IMPERSONATION_LEVEL (0x80070542)
errors for system-level on-demand update checks.

BUG=496313
R=ganesh@chromium.org, pkasting@chromium.org

Review URL: https://codereview.chromium.org/1160273006

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#334055}

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